The present invention generally relates to the field of frequency-conversion receivers. More specifically, it relates to a system and method for frequency multiplexing in frequency-conversion receivers.
Frequency-conversion receivers are used in various electronic devices, such as televisions (TV), radios for transmission and reception of RF signals at particular frequencies. A frequency-conversion receiver receives transmitted signals for example, a band of radio frequency (RF) signals carrying multiple channels and converts the RF signals to signals of a different frequency. The frequency-conversion receiver processes these transmitted signals to provide the desired output signals to the demodulator. The demodulator demodulates the desired output signals to extract information. Examples of frequency-conversion receivers include a heterodyne receiver, a super heterodyne receiver, a double-conversion receiver, and the like.
The frequency-conversion receiver includes a mixer and a filter. The mixer converts the band of RF signals to an intermediate frequency (IF) signal. The IF signal is filtered by using the filter and amplified to provide the desired output IF signal. The filtering removes unwanted signals that need to be rejected from the output IF signals. Examples of filters include SAW filters, variable band pass filters and the like. Since IF signals are easy to filter, amplify and process, the RF signals are converted to IF signals. However, the available IF filters have low bandwidth, which restricts the frequency conversion of wideband IF signals. To process wideband IF signals wide-bandwidth filters are needed, which have high insertion loss. High insertion loss filters cause poor signal-to-noise ratio, which limits the lower end of receiver dynamic range. Further, the processing of wideband signals cause high inter-modulation distortion, which sets the limit on the high end of receiver dynamic range. In light of the foregoing discussion, there is a need for a system and method for frequency conversion that allows transmission of large number of channels (i.e. have a wide bandwidth) with minimum noise and distortion.